(i) Field of the invention
The present invention relates to a base (holding device) which, though also suitable for other applications, has been specially designed for installing aerials, and more particularly, for installing aerials onto the roof of a motor vehicle.
(ii) Brief Description of the Prior Art
As is already well known mounting bases for aerials allow rotation thereof, within a relatively wide arc, and ensure their retention by friction means in the desired angular position. Rotation of the aerial must be effected within a given rotation torque, which must be maintained within admissible tolerance limits throughout the life of the product. Furthermore, this rotation torque must be such that the user is able to adjust the position of the aerial, without recourse to any tool, thereby positioning the aerial at any angle possible within the admissible arc.
This is achieved by means of a controlled grip between the fixed part, or base, and the moving part, or aerial, in such a way that the friction between both generates the rotation torque, and defines the retention in a position at any given time. This controlled grip is usually achieved by means of a bolt which passes freely through both components screwing into a nut which is held in position by means of a rotation-lock arrangement, with interpolation of a standardized flexible washer (type DIN 2093) to maintain the rotation torque throughout the admissible arc of rotation. Since both components, in contact and subject to friction, are also required to achieve the continuity of electrical contact allowing the passage of the radio signal, it is not possible to interpose between them any non-conducting articles.
These known mounting bases are subject to two principal disadvantages.
The first of the disadvantages lies in the fact that the rotation torque obtained depends directly on the gripping torque of the bolt. In order to obtain a pre-set rotation torque and to maintain it within the admissible tolerances, a perfectly controlled gripping torque has to be imparted to the bolt, thereby necessitating the use of expensive gripping and control means, yet without the guarantee of complete reliability, since there are other factors such as thread profile, alignments, etc. which can cause variations in the correlation between gripping torque and rotation torque.
The second of the disadvantages resides in the fact that because the rotation torque is based upon friction between two metal components subjected to considerable pressure, the components are subject to wear due to rotational movements of the moving component. Initially this wear can be remedied by provision of the flexible washer already referred to, but since its compression is very limited, after a few operations its function is lost thus resulting in the loss of grip and thereby the capacity of the moving component to be retained in its previously adjusted angular position.